Oral prescription medical foods have long been used in hospital settings but are also appropriate therapies for gastrointestinal disorders in outpatient medical practice. Oral serum-derived bovine immunoglobulin/protein isolate (SBI) has been shown in clinical studies to reduce loose stools and improve stool consistency as well as other symptoms (i.e., abdominal pain, bloating, and urgency) in patients with irritable bowel syndrome with diarrhea (IBS-D) and human immunodeficiency virus-associated enteropathy. This case series reports the outcomes of 14 IBS patients who received SBI as an addition to standard of care at an individual physician's clinical practice. The patients: 2 IBS with constipation (IBS-C), 7 IBS-D, 2 mixed diarrhea and constipation IBS (IBS-M) and 3 undefined IBS (IBS-U; also described by some physicians as IBS-Bloating), ranged in age from 22-87 years. SBI (5 g or 10 g daily dose) was added to the patient's current standard care and followed for several weeks to determine if symptoms were improved with the addition of SBI. Overall, 12 of the 14 patients indicated some level of improvement through direct questioning of the patients regarding changes from the prior visit. One IBS-Bloating patient had a resolution of symptoms and two patients (1 IBS-Bloating and 1 IBS-C) discontinued therapy because of insufficient relief. The 12 patients who continued on therapy reported an overall improvement in symptoms with better stool consistency, decreased frequency as well as reductions in abdominal pain, bloating, distention, and incontinence. In most cases, therapeutic effects of SBI were seen within the first four weeks of therapy with continued improvements at subsequent visits. SBI has a multifaceted mechanism of action and may help to manage IBS by providing a distinct protein source required to normalize bowel function, gastrointestinal microbiota, and nutritionally enhance tight junction protein expression between intestinal epithelial cells. SBI as a medical food provides a safe option for patients with IBS-D but may have application in other forms of IBS.